Hello Dave,
Many thanks for pointing us to this range of products. They look
very smart and their price is so low, they can be replaced without making an
appointment with your bank manager for a 2nd mortgage.
Melting connectors?
·
When I studied for my electrical and electronics engineering
degree (early 1960s), we were told to restrict current flow in enclosed
conductors – in motors, generators, transformers, ducting – to 1000 A / sq in.
When we followed this rule, the copper never got more than mildly warm.
·
Later, when I was Production Manager of a distribution
transformer manufacturer (late 1960s), we sometimes allowed 1500 A / sq in, but
these transformers were in oil-filled tanks and had cooling tubes on the outside
of the tank to carry convected oil.
·
When I was a university lecturer in the UK (1970s and 1980s), I
mentioned the rubberiness of the Amp / sq in rule, but found British
transformer manufacturers for consumer goods using the same rule.
·
At the same time, I found that European manufacturers were
flooding the British market with goods where the transformers were running at
2000 A /sq in, and they got quite warm; there was a major market in replacement
transformers. Clearly, accountants and marketing people were now in charge of
transformer design, and the shape of the final transformer depended on the
relative spot prices of copper and grain-oriented steel, and the softness of
the consumer market for early product obsolescence.
·
When I returned to Australia (early 1990s), I found the local
market flooded with American transformer products where the design rule seemed
to be 2500 A /sq in. These devices could give the uninitiated quite serious
burns.
·
A would-be radio amateur asked me to look at the wiring on board
his million-dollar yacht. Though the cross sectional area of the wiring was
more than adequate, the terminating lugs had not been tightened down properly.
There were signs of connector blocks overheating and burning the wooden
mounting plate. It’s a wonder the boat had not burned to its Plimsoll line.
So, I suggest you look carefully at the cross-sectional area of
the serious current carrying connector parts, and how well you tighten those *little
screw terminals*.
Power tube?
One of the discussants from the cheap seats, commented on the
use of *power tube* as in the 4th bullet point in the *About
this item* text. This product was designed in a country where English is
the 42nd language, and the people charged with making an English
translation available may have English as their 3rd or 4th
language. I reckon that American self-righteous beliefs in their world superiority
with technical English are misplaced, and a smidgin of humility toward people
struggling with the multi-headed Hydra called the English language, is due.
The concept expressed in that 4th bullet point is essentially
correct, though it is the final power pass transistor that will fail when the
product of emf (Voltage) and current exceeds its rated specification, ie, the
heat generated exceeds the ability of the heatsink to maintain temperature
below die melt temperature.
Cheers, me ole mate, Brian
From:
[email protected] [mailto:[email protected]] On Behalf
Of David Stinson
Sent: Friday, 20 May 2022 12:34 AM
To: milsurplus@mailman; ARC-5
Subject: [ARC5] Why Don't They Melt?
I
have a project brewing which requires 32 Volts
at 10 amps. I intend to use a 600 Watt DC/DC
converter which will input anything from 12 to 60
volts unregulated and output a constant 32 volts.
Here's one such:
https://www.amazon.com/Dasiter-Converter-12-60V-Step-up-Transformer/dp/B08B63RYD6/
If I input 12 volts, I'm gonna need about 26 amps plus or minus
to get 32 volts at 10 amps out. That's half the rated power
this thing specs.
Trouble is- Look at those input and output connectors.
How on earth can one pull 320 Watts, much less 600, through
those little screw terminals?? I'll probably go 28V in just
to knock the input current down to something reasonable.
Dave S.
